Infrared spectroscopic determination of the gas-phase thermal decomposition products of metal-ethyldithiocarbonate complexes

Head-space analysis by gas-phase infrared spectroscopy (HAGIS) allows the facile examination of the decomposition mechanisms of the metal xanthates [metal-(O-alkyldithiocarbonates], Fe(EtOCS2)(3), Zn(EtOCS2)(2), Cu(EtOCS2), Pb(EtOCS2)(2) and Ni(EtOCS2)(2), over the temperature range 25-120 degrees C. These metal xanthates fall into two groups based on the generation of the primary gaseous decomposition products, CS2, COS and CO2. The first group, consisting of Fe(III) and Zn(II) xanthates, decompose readily, forming mostly CS2 and COS in a constant ratio and leaving, initially, a metal-alkoxide residue. In the second group, decomposition is relatively small, generating CO2 and COS, with the proportion of COS increasing as the temperature increases and CS2 formation occurring only at the upper end of the temperature range. The residue is more of a metal-thioalkyl species in this case. Presumably, CO2 is formed by re-insertion of COS into a metal alkoxide and elimination of CO2, leaving a thioalkyl moiety. Volatile metal-xanthates are probably observed in the gas-phase, allowing examination of the changes concomitant to the vaporization of the discrete metal xanthates from network or partially associated solids. (C) 1997 Elsevier Science B.V.